Wood truss arrangement

ABSTRACT

A wood truss, or lattice girder, arrangement with finger scarfing of only alternate generally parallel members to the chords, with oppositely inclined generally parallel web members only to the inclined webs. Material reduction of web to chord to web transference achieved producing a stronger truss with webs of the same size.

United States Patent [s] 3,702,050

Price [451 Nov. 7, 1972 [54] WOOD TRUSS ARRANGEMENT 3,262,723 7/1966 Strickler..... 287/2092 T [72] Inventor, George E Price, west Vancouver, 3,452,502 7/1969 Price s2/693 British Columbia Canada 3,480,054 ll/ 1969 Marian 287/2092 T ssignee acl c 0a pe Lmlted, Van OTHER PUBLICATIONS couver, British Columbia, Canada Filed: Jan. 4, 1971 Appl. No.: 103,884

Related U.S. Application Data Continuation of Ser. No. 830,450, Jan. 4, 1969, abandoned.

Foreign Application Priority Data June 1,1967

u s. ci. l.s2/093, 287/2092 T im. cl. ..1:04c 3/02, E04c 3/42 Field of Search ..52/642, 690-695,

References Cited UNITED STATES PATENTS 4/1921 Carpenter ..52/695 Attorney- Brian J. Wood Canada .991,946

Aircraft Engineering, May 1950, Vol. XXII, Issue No. 255, Page 147 Primary Examiner-Frank L. Abbott Assistant Examiner-James L. Ridgill, Jr.

[5 7] ABSTRACT A wood truss, or lattice girder, arrangement with finger scarng of only alternate generally parallel members to the chords, with oppositely inclined generally parallel web members only to the inclined webs. Material reduction of web to chord to web transference achieved producing a stronger truss with webs of the same size.

2 Claims, 4 Drawing Figures WOOD TRUSS ARRANGEMENT This application is a continuation of application Ser.

No. 830,450, filed Jan, 4,1969, and now abandoned.

FIELD OF THE INVENTION BACKGROUND OF THE INVENTION AND PRIOR ART British Pat. No. 733,288 issued to Gerlach and published in 1955 teaches a wooden lattice girder in which the lattice members are finger scarfed together, with the finger scarfed members extending through the cords. A Swiss Pat. No. 306,573 issued to Kampf in 1955 teaches a lattice girder construction resembling that of Gerlachs in that the lattice members extend through the cords. A Federal German Pat. No. 1,154,253 of 1963 also to Gerlach teaches construction in which, although differing from his British patent above, web members are joined to one another with the joint extending through the cord. U.S. Pat. No. 2,780,842 issued toHess in 1957 also shows web connected to adjoining web, with the join extending through the cord or, alternatively, through a bloc secured to the cord.

SUMMARY F THE INVENTION ln all the known constructions above stress transference is largely web to cord to web. A United States patent application Ser. No. 474,786 now U.S. Pat. No. 3,452,502 issued July l, 1969 of the present inventor George E. Price assignee, in a Wood Truss Joint was allowed 30 Oct. 1968 but has not yet issued. This teaches a wood truss joint wherein, while there is still some transference of stress from web to cord to web, this is materially less than in the known constructions above. Price has discovered that further reduction of stress transference fromweb to cord to web is attained by finger scarfing only alternate generally parallel web members to the upper and lower cords, and by finger scarf'mg oppositely inclined webs only to the inclined webs aforesaid.

All of the joints discussed here are glue b'onded according to known procedures. The stresses and stress patterns existing in, and in the vicinity of, joints of this kind are exceedingly complex and are difficult to analyze. While knowledge of these joints is incomplete, there is indication that where webs which are connected to the cords and to other webs are subject to tensile stress, and the intervening webs which are connected only to other webs are subject to compressive stress, advantage results. This advantage is attributed to material reduction of tensile stress perpendicular to the wood grain. Thus a wood truss arrangement according to the present invention can produce a stronger truss than heretofore with webs of the same size.

A detail description following related to drawings gives examplification of preferred embodiment of the invention which, however, is capable of expression in joints other than those particularly described and illustrated.

DESCRIPTION OF THE DRAWINGS FIG.'1 is an isometric'drawing of a part of an assembled truss constructed according to the invention,

FIG. 2 is a detail section on 2-2 of FIG. l, FIG. 3 is a detailed section on 3--3 of FIG. 1,

FIG. 4 is a fragmented isometric drawing showing alternate web to web finger scarfmg.

PREFERRED EMBODIMENT Description of FIG. 1.

A fragmented truss, generally 10, has an upper chord ll spaced from a lower chord 12, by an inclined interconnected web member 13 and an oppositely inclined interconned web member 14. The web member 13 is finger scarfed at a lower end to the lower chord I2 as indicated at 15, an upper end being finger scarfed to the upper chord 1l as indicated at 16.

The oppositely inclined web 14 has a lower end finger scarfed to the inclined web I3 adjacent to, and clear of, the lower chord at 17.

A second inclined web member 19, generally parallel to the web 13, is finger scarfed to the lower and upper chords as shown at 2l and 22.

The oppositely inclined web 14 has an upper end finger scarfed to the web 19 at 23.

A further web member 24 oppositely inclined to the webs 13 and 14 appears fragmented in FIG. 1. A lower end of this web 24 is fingerscarfed at 25 to the inclined web 14 adjacent to, and clear of the lower chord 12.

In FIG. l the oppositely inclined webs 24, 14, are shown fingerscarfed to the inclined webs 14, 13, well Clear of the lower chord l2. This is for clarity of illustration, in actuality the members 24 and 17 are just clear of the chord.

FINGER SCARFING CONSIDERATIONS AND REFERENCE TO FIGS. 2 AND 3.

As shown in FIGS. 2 and 3, the finger scarfing is substantially triangular in section. For'practical reasons the fingers are normally made with flat butts (not shown) at ridges and valleys. Usually the scarfing has a pitch of about 1:6, that is to say that the included angle at the apex of the finger is about 18. Nevertheless, the invention is of value in the limit where the included angle at the apex is zero, that is to say where the joint becomes a rectangular mortice and tenon.

As described, the webs are connected both to the chord and other webs or to other webs only. It will be apparent that, at ends of the truss, end webs must be connected to the chord only.

The pitch of the finger scarfing has been given as being about 1:6, it has been found that this figure is satisfactory and gives results approaching optimum. It has also been pointed out that large variation in pitch still results in operable joints, practical effective limits of pitch are generally within the approximate limit 1:5 t0 1:7.

FIG. 4 ALTERNATIVE In FIG. 4 a web member 24.1 has finger scarfing to the web 19 differing from the web to web finger scarfing above. The web 24.1 is chamfered as shown at 26 'before scarfing so as to provide a flat adjacent to an upper surface 27 of the lower chord 12. This results in lengthening of web members such as 24, 14, with some pair of adjacent first members scarfed to a side edge of each of said adjacent pair of first members adjacent but spaced from the cords so that load is transmitted to the Voppositely inclined web members only through the inclined first web members. 2. A wood truss as claimed in claim l in which the finger scartmg of the oppositely inclined web members is chamfered so that said finger scarring is reduced in length to a length of about three quarters the depth of said oppositely inclined members.

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1. A wood truss including: a. spaced upper and lower cords, b. a plurality of inclined first web members scarfed at each end in facing cord sides, said first web members having substantially the same inclination, c. an oppositely inclined web member between each pair of adjacent first members scarfed to a side edge of each of said adjacent pair of first members adjacent but spaced from the cords so that lOad is transmitted to the oppositely inclined web members only through the inclined first web members.
 2. A wood truss as claimed in claim 1 in which the finger scarfing of the oppositely inclined web members is chamfered so that said finger scarfing is reduced in length to a length of about three quarters the depth of said oppositely inclined members. 